1. Field
A material for an organic optoelectronic device, an organic light emitting diode, and a display device including the organic light emitting diode are disclosed.
2. Description of the Related Art
An organic photoelectric device is a device requiring a charge exchange between an electrode and an organic material by using holes or electrons.
An organic optoelectronic device may be classified in accordance with its driving principles. A first organic optoelectronic device is an electronic device driven as follows: excitons are generated in an organic material layer by photons from an external light source, the excitons are separated into electrons and holes, and the electrons and holes are transferred to different electrodes as a current source (voltage source).
A second organic optoelectronic device is an electronic device driven as follows: a voltage or a current is applied to at least two electrodes to inject holes and/or electrons into an organic material semiconductor positioned at an interface of the electrodes, and the device is driven by the injected electrons and holes.
Examples of the organic optoelectronic device include an organic light emitting diode, an organic solar cell, an organic photoconductor drum, an organic transistor, and the like, which require a hole injecting or transport material, an electron injecting or transport material, or a light emitting material.
Particularly, an organic light emitting diode (“OLED”) has recently drawn attention due to an increasing demand for flat panel displays. In general, organic light emission refers to conversion of electrical energy into photo-energy.
Such an organic light emitting diode converts electrical energy into light by applying a current to an organic light emitting material. It has a structure in which a functional organic material layer is interposed between an anode and a cathode. The organic material layer includes a multi-layer including different materials, for example a hole injection layer (“HIL”), a hole transport layer (“HTL”), an emission layer, an electron transport layer (“ETL”), and an electron injection layer (“EIL”), in order to improve efficiency and stability of an organic light emitting diode.
In such an organic light emitting diode, when a voltage is applied between an anode and a cathode, holes from the anode and electrons from the cathode are injected to an organic material layer and recombined to generate excitons having high energy. The generated excitons generate light having certain wavelengths while shifting to a ground state.
Recently, it has become known that a phosphorescent light emitting material may be used for a light emitting material of an organic light emitting diode in addition to the fluorescent light emitting material. Such a phosphorescent material emits lights by transporting the electrons from a ground state to an exited state, non-radiance transiting of a singlet exciton to a triplet exciton through intersystem crossing, and transiting a triplet exciton to a ground state to emit light.
As described above, in an organic light emitting diode, an organic material layer includes a light emitting material and a charge transport material, for example a hole injection material, a hole transport material, an electron transport material, an electron injection material, and the like.
The light emitting material is classified as blue, green, and red light emitting materials according to emitted colors, and yellow and orange light emitting materials to emit colors approaching natural colors.
When one material is used as a light emitting material, a maximum light emitting wavelength is shifted to a long wavelength or color purity decreases because of interactions between molecules, or device efficiency decreases because of a light emitting quenching effect. Therefore, a host/dopant system is included as a light emitting material in order to improve color purity and increase luminous efficiency and stability through energy transfer.
In order to achieve excellent performance in an organic light emitting diode, a material constituting an organic material layer, for example a hole injection material, a hole transport material, a light emitting material, an electron transport material, an electron injection material, and a light emitting material such as a host and/or a dopant, should be stable and have good efficiency. However, development of an organic material layer forming material for an organic light emitting diode has thus far not been entirely satisfactory and thus there is a need for a novel material. This material development is also required for other organic optoelectronic devices.
A low molecular organic light emitting diode is manufactured as a thin film in a vacuum deposition method, and can have good efficiency and life-span performance. A polymer organic light emitting diode manufactured in an Inkjet or spin coating method has an advantage of low initial cost and being applicable to a large display.
Both low molecular organic light emitting and polymer organic light emitting diodes have advantages of self-light emission, high speed response, wide viewing angle, ultra-thinness, high image quality, durability, large driving temperature range, and the like. In particular, they have good visibility due to the self-light emission characteristic compared with a conventional LCD (liquid crystal display), and have an advantage of decreasing thickness and weight of an LCD by up to a third, because they do not need a backlight.
In addition, since they have a response speed of a microsecond unit, which is 1,000 times faster than an LCD, they can realize a perfect motion picture without an after-image. Based on these advantages, they have been developed to have a remarkable 80 times the efficiency and more than 100 times the life-span since they first came out in the late 1980's. Recently, they have become rapidly larger such that a 40-inch organic light emitting diode panel is now possible.
They are simultaneously required to have improved luminous efficiency and life-span in order to be larger. Such luminous efficiency requires smooth combination between holes and electrons in an emission layer.